Tunnel drive performance issue

The various drag determination methods are a check on the prop curve. The VW 1.9l TDI motor develops maximum torque around 1800rpm. It should be able to produce around 40kW at 2100rpm if it was in good order.

The 14 X 17 prop cannot absorb more power than 16kW at 1050rpm. There is a huge gap between 16kW and 40kW.

The engines get to 2100rpm OK and then do nothing more as the throttles are pressed. You would normally expect black smoke if the props were causing the engines to labour.

The comparison between the 7307N and the 4600N brings in other factors that have some relevance. The 4600N assumes clean hull and no appendages with a weight of 3.5t and no windage - so it is certainly optimistic. The 7307N relates to a time when the boat had drives legs and probably somewhat heavier. It also assumes the original engines actually produced 130HP and there is an assumption of the props being 55% efficient.

The drag determination I have used for displacement mode is analytical based on actual shape not empirical. Again it assumes a clean hull.

To me everything points to the engines not developing anywhere near their rated power. I would be having a very close look at all the connections to the sensors and also get a VW engine expert to bring his computer around and check out the engine controller. I would do this before I threw my hands in the air and accepted that all the time and effort I had put into modifying the hulls was an absolute waste of time. I would do this before I start changing the prop pitch. I would want to know I had exhausted every avenue to understand the performance gap.

Arguing about the accuracy of drag results being 20 or even 50% in error is mental ************ when the engines are performing something like 30% of their rating.

Rick W

 

"...Arguing about the accuracy of drag results being 20 or 50% in error is mental ************.."

believing them, is the ************!

 

"..The drag determination I have used for displacement mode is analytical based on actual shape not empirical..."

Oh dear, here we go again...not understanding the program and its limitations one is using!

I'm sure beackmo will also point out, as any competent naval architect/engineer will know that these methods are a statistical regression of the results of a number of tank tests, where the hull forms are not a systematic form, but are similar in generic terms, ie just planing or semi-displacement. The S method is a slight improvement insofar that it is a mixture of analytical procedure and empirical tank data.

The only 'analytical' part is the method of obtaining a 'trend' line based upon the empirical data.

 

CDK
Here is a bit more on limp mode. Seems to be set to limit the TDI engine speed to 2000rpm if it is invoked. There are many causes apparently and you probably need a VW computer to see if it is actually occurring.

It could be something related to the engine labouring and then protecting itself. It could be something set incorrectly so it is over protection.

Rick W

 

I read the marinizing thread and understood that the original ECU was disengaged?

In a car world there would 2 apparent causes for this in a 1.9tdi of this era:
a) Faulty MAF - ECU will not feed enough fuel
b) Faulty turbo actuator valve (N75)

But if the ECU is stripped out, there should be no fault modes or MAF-problems, if the pump control is at full there should be massive smoke when the engine is overloaded.

 

I said earlier I have a working tunnel drive....I thought CDK would pick me up on it ....I bought a jetless jetski and being an outboard pod man thought a 90 deg step under the boat about 2 ft from the transom would shoot the water up 6 in into the tunnel .....how wrong can you be ....boat rose up 1/2 planing on the sides of the hull and lifted the prop out the water ......so I fitted a very shallow 15 deg rise into the tunnel ..ply and foam ..well the boat is only 3 m long ....and all was well ...this is what Baekao is suggesting in his modification drawing .....

Now children stop fighting or I will send michael Jackson in to sort you out

 

Iiki
I have not seen any reference to removing the ECU. I guess CDK will confirm or otherwise.

To me there seems to be too much coincidence with the engines being limited to producing about 12kW and stuck at 2100rpm. Not what you would expect from an engine with its low down torque and power rating up around 60kW.

Rick W

 

I think he did. He cleaned up the entry and speed dropped from 14kts to 10kts. The props are probably working in normal flow now but are bogging the engines down.

I doubt if the boost is working as the motors are limiting to about 12kW and 2100rpm. I thinking when it asks for boost something does not work and the ECU goes into limp mode. That is the best explanation I can come up with given what he is seeing.

There are some interesting stories on trying to track down the cause of limp mode in the turbo diesels. It is not limited to VW either. This one would make a sane person insane:
http://www.benzworld.org/forums/w901-905-sprinter/1358263-313-cdi-power-loss-limp-mode.html

Rick W

 

Hi Voyager,

Nice to see that you are still observing the developments.

I have not forgotten our earlier communications and know you have been skeptical from the start. But if you get an idea that you think is feasible, the only way to make sure is construct it and test it. Of course it would have been much simpler following known paths but then you never discover a new one.
Two large 4-stroke outboards would have been a much quicker solution, but I love the feeling of uncharted territory.

About 10 years ago I dedicated some time learning the details of LCD and TFT screens and concluded that backlighting a screen with a fluorescent lamp is primitive and energy wasting, especially when you want to display a black screen. I thought up a construction with white LED's and acrylic glass diffusors, where the screen area is divided in sectors, so you need to illuminate only relevant parts. And now the new generation of ultraflat Samsung TV sets does exactly that.

My oil filled stern tubes with double seals behind the props and the chamber filled with silicone oil was greeted with little enthousiasm on this forum, yet they are in place for three years now and are 100% successful. The bearing carriers, held in place by an O-ring compressed in a triangular groove, did not pop out like experts predicted.

At the present state, the tunnels provide a very efficient way to propel my boat. The temperature here is over 30 C. at 9 AM already, the shores are paved with white, red and brown flesh and boat owners endlessly drift in circles near the fuel station. I filled my tank one and a half year ago, make regular trips to beaches nearby and am certain that the fuel will last to the end of this season.
The only wish left is to reach planing speed or get as close as possible.

Before I started work on my boat, I read all I could find, Levi, Saro, Arneson, Simplicity Marine and several others, then decided to go my own way. It may eventually come to 4 blade surface piercing props. Levi has nothing under 17", but others will. Or I re-adjust my goals and be satisfied with displacement. Recently I saw same sort of tugboat with a tunnel so large two guys could have played cards in it: that one certainly couldn't plane.

But the first target is to get the horse-powers back that seem to be lost now.

Rgds,
Cornelis

 

As I pointed out in the past (Post 52 and 62 here, more in the other threads), these ARE NOT TDI ENGINES! My little machines are 1.9TD's, engine type ABL, with mechanical fuel injection, mechanically limited Garrett T3 turbo chargers and INDIRECT ignition. One came from a 1999 transporter van used by the ANWB (Holland's national automobile club) and was immaculately serviced, the other from an unknown van and was neglected.
There is and was no ECU, the only modification I made to the fuel injection was removing the EGR valves and using the existing Volvo Penta fuel filters/water separators instead of the vehicle ones.

 

If you send me or post a photo of the injection pump I will let you know how to check they are getting equal fuel and boost and if neccessary how to raise the fuel /boost ...all the pumps are made for a variety of engines and are easily adjustable ..which is why if these are second hand they may have been fiddled with in the past

 

A couple of questions:

Do you have any idea what torque the 1.9l IDI should produce at 2100rpm if in good shape?

Is there anything in the air or fuel supply that could limit power output to around 12kW at 2100rpm?

Rick W

 

Well I was trying to help CDK ....yourstatement worries me " anything in the air supply " ....this is a diesel mate there is nothing between the valves and the air inlet except the turbo to restict air unless CDK has put excessive pipework or silly size air filters on it ....Petrol heads should not try to diagnose diesels ....

As for output about 140 ft lb at 2000 rpm shounds about right but if the power valve or trubo pressure has been messed with could be very low or + 25% if I had breathed on it ...!!! ( on another forum I have 11000 views on my post on how to get +25 % more from your land rover diesel )

I await CDK s photos or comments ......

 

Explain the power valve and how it could be messed with. How low can the power be if it is badly messed with. It also has to be the same issue with both engines although one is a bit livelier than the other.

The props will require only 110N to run at 1050rpm so 55N at the engines. They should be able to do well over this. From what I can glean they are rated at 150N at 2400rpm. Ample to spin 14X17 props well over 1050rpm.

I think CDK is out in the boat today with guests so he might be a while before he gets back. I could do with some of the nice warm weather he is enjoying.

Rick W

 

The waste-gate ("power valve") and fuel setting issues have been dealt with in the thread "DIY tunnel drive" under Propulsion. There you also find reasonably adequate power figures for the engines in standard condition, and conclusions as per the power absorbtion of the propellers as today. We arrived at a max power of ~15 kW (20 hp), which is close to RW's estimate here.

I agree with pistnbroke that there is a possibility that the pumps have been fiddled with, but the fact that both are seeming to produce similar rpm's contradicts this (not two fiddlers arrive at the same concert). If normal torque curves are convex upwards, engines with waste-gates often have a concave part at the low speed end. This is seriously aggravated by anything from exhaust back pressure to dirty fuel filters. With propeller torque curve close to engine torque in this region, there is little margin between success and trouble.

This effect is often seen when a "wg-engine" is used for heavy towing; the propeller torque curve is steeper than normal, and the engine is stuck in the "low speed valley". In a road vehicle, this behaviour is not observed, because you would have stepped down a number of gears long before the engine was bogged down. So CDK's problem here is not unique or due to any black magic, or bad craftsmanship; it is a classic matching problem (and some installation issues).